1. National Engineering Research Center for Biomaterials and College of ChemistrySichuan University 29 Wangjiang Road Chengdu 610064 China
2. West China HospitalSichuan University 37 Guo Xue Xiang Chengdu 610041 China
3. Materials Science and Technology of Polymers and the MESA+ Institute for NanotechnologyUniversity of Twente P.O. Box 217 7500 AE Enschede The Netherlands